Millimeter wave radio communications (corresponding to radio frequencies above roughly 10 GHz) afford substantially higher data capacity than their longer wavelength counterparts. Consequently, communications at such frequencies are one of the central enhancements being adopted in the 3rd generation partnership project (3GPP) standards for the next generation, so-called 5G, mobile telecommunication networks. While 5G will provide data rates in the 10 Mbit/s-1 Gbit/s range, shorter wavelength radio communications suffer high variability in radio link quality. Indeed, buildings, automobiles and even the human body can interfere with millimeter wave radio, thus diminishing the quality of the affected radio links.
FIG. 9 depicts a blocker 10 being interposed between user equipment (UE) 110 (also referred to as a wireless transmit and receive unit (WTRU)) and a transmitter (not illustrated). As illustrated in the figure, blocker 10 has a dimension W that is transverse to the directionality of the UE antenna, is located a distance D from UE 20 and is moving at velocity V. Table 30 illustrates radio link outage intervals for different types of blockers 10, where items 32 may correspond to a large truck, items 34 may correspond to a passenger automobile and item 36 may correspond to a human body. As FIG. 9 demonstrates, considerable radio link outage may occur in the presence of these blockers.
FIG. 10 illustrates another blockage scenario in which passenger automobiles 12a-12d, representatively referred to herein as automobile(s) 12, are moving at a velocity V and maintaining a distance D safe between one automobile 12 to the next. In such a case, the blockage is intermittent, with the time between successive blockage events being illustrated in Table 40.
While physical layer interference is entirely expected in the presence of blockers, what is less expected is the dramatic effect on the transport layer that such blockage entails. FIG. 11 illustrates the effect on data rate 50 and TCP sender window size (MSS per the Transport Control Protocol (TCP)) 60 responsive to blockage at blocking intervals 55a-55e, representatively referred, to herein as blocking interval(s) 55. As illustrated in the figure, there is significant degradation in data throughput in the presence of blockers, but such degradation is attributable not just by a drop in radio signal strength or quality. Indeed, radio blockage has a profound impact on data transport such as by TCP as demonstrated by Table 1 below.
TABLE 1BlockageTCPBlockage ModelRatioThroughputTCP DegradationNo Blocking0%807 Mbps0%0.1 s blocking every 5 s2%712 Mbps−12%0.2 s blocking every 5 s4%371 Mbps−54%1 s blocking every 5 s20%229 Mbps−72%
The causes of such dramatic drop in TCP throughput over the corresponding blockage ratio include TCP sender retransmission timeout (RTO) and congestion control mechanisms was triggered such as window shrinking. Overcoming such degradation in TCP throughput is a subject of ongoing research and engineering efforts.